Highly efficient 2d/3d switchable display device

A switchable display device comprising:

• a light source unit;
• a polarization switching unit which switches light from the light source unit to one of first polarized light and second polarized light, which is perpendicular to the first polarized light;
• a parallax barrier comprising slits and barriers that are alternately arranged, wherein the slits transmit incident light and the barriers transmit one of the first polarized light and the second polarized light and reflect the other of the first polarized light and the second polarized light;
• and
• a display panel which modulates light transmitted through the parallax barrier in response to an image signal to create an image,
• wherein the switchable display device controls an electric signal applied to the polarization switching unit so that a two-dimensional (2D) image and a three-dimensional (3D) image are switched to each other.